The genetic background for the onset of cancer is alterations in proto-oncogenes, oncogenes and tumour suppressor genes. Proto-oncogenes are normal genes of the cell which have the potential of becoming oncogenes. All oncogenes code for and function through a protein. In the majority of cases they have been shown to be components of signal transduction pathways. Oncogenes arise in nature from proto-oncogenes through point mutations or translocations, thereby resulting in a transformed state of the cell harbouring the mutation. Cancer develops through a multi-step process involving several mutational events in oncogenes and tumour suppressor cells.
In its simplest form, a single base substitution in a proto-oncogene may cause the encoded protein to differ in one amino acid.
In experimental models involving murine tumours, it has been shown that point mutations in intracellular “self”-proteins may give rise to tumour rejection antigens consisting of peptides differing in a single amino acid from the normal peptide. The T cells recognizing these peptides in the context of major histocompatibility (MHC) molecules on the surface of the tumour cells are capable of killing the tumour cells and thus rejecting the tumour from the host. (Boon, T. et al, Cell 1989, Vol. 58, p. 293-303)
In the last three decades, particular effort has been devoted to the analysis of antibodies to human tumour antigens. It has been suggested that such antibodies could be used both for diagnostic and therapeutic purposes, for instance in connection with an anti-cancer agent. One problem is that antibodies can only bind to tumour antigens that are exposed on the surface of tumour cells. For this reason the efforts to produce a cancer treatment based on the immune system of the body has been less successful than expected.
Antibodies typically recognise free antigens in native conformation and can potentially recognise almost any site exposed on the antigen surface. In contrast to the antibodies produced by the B cells, T cells recognise antigens only in the context of MHC molecules, designated HLA (human leukocyte antigen) in humans, and only after appropriate antigen processing, usually consisting of proteolytic fragmentation of the protein, resulting in peptides that fit into the groove of the MHC molecules. This enables cells to recognise peptides derived from intracellular proteins. T cells can thus recognise aberrant peptides derived from anywhere in the tumour cell, when displayed on the surface of the tumour cell by MHC molecules. The T cell can subsequently be activated to eliminate the tumour cell harbouring the aberrant peptide.
T cells may control the development and growth of cancer by a variety of mechanisms. Cytotoxic T cells, both HLA class I restricted CD8+ and HLA Class II restricted CD4+, may directly kill tumour cells carrying the appropriate tumour antigens. CD4+ helper T cells are needed for induction and maintenance of cytotoxic T cell responses as well as for antibody responses, and for inducing macrophage and lymphokine-activated killer cell (LAK cell) killing.
Many oncogenes and their protein products have been identified. In addition, it has been shown that the cell repertoire of a healthy person includes T cells with specificity against a synthetic peptide fragment derived from one p21 RAS oncogene product, when presented on an appropriate HLA molecule. Furthermore, it is anticipated that approximately 20% of all cancers are associated with a mutation in the RAS oncogene.
There are great concerns about using peptide mixtures for vaccination of patients due to the risk that some of the peptides in the mixture are immunodominant and thus suppress the HLA presentation of the other peptides (Pion S, et al., Blood, 1999 Feb. 1; 93(3): p952-62). From experiments performed in vitro, it is known that various mutated RAS peptides may compete for binding to the HLA molecule responsible for presentation to the relevant T cells and that peptides of the same length, but representing different mutations may inhibit the binding and recognition of a peptide representing another mutation with different degrees of efficacy (T. Gedde-Dahl III et al., Human Immunol. 1994, 33, p. 266-274, and B. H. Johanssen et al., Scand. J. Immunol., 1994, 33, p. 607-612). From these facts, the immunodominance issue has been regarded as a problem for mutated RAS peptide vaccines.
WO 92/14756 discloses synthetic peptides and fragments of oncogene protein products which elicit T cell immunity, for use in vaccines against cancers associated with RAS and compositions for the treatment of cancer. The peptides must correspond to an active fragment of the oncogene as presented by the cancer cell and include a mutation in one or more positions corresponding to the oncogene mutation. This document discloses mutations at positions 12, 13 and 61 of the RAS protein and specifically discloses only G12A, G12V, G12C, G12S, G12K, G12D, G12R, Q61R, Q61K, Q61L, Q61H, G13V and G13D mutations. In addition, while this document mentions that vaccines may comprise a selection of peptides having the most common mutations found in oncogene proteins, it does not suggest any specific combinations.
WO 00/66153 discusses synthetic peptide mixtures which elicit T cell immunity for use in cancer vaccines. The peptide mixtures consist of RAS p21 mutant peptides and this document specifically discloses only G12A, G12C, G12D, G12R, G12S, G12V, Q61H, Q61K, Q61L, Q61R and G13D mutations. This document also discloses that the immune response elicited by a cocktail of peptides was significantly higher than that elicited by a single peptide; however, it does not suggest that any other combinations of peptides other than those specifically disclosed therein may be useful.
GB 2328689 discloses that a peptide capable of inducing specific cytotoxic T cell responses (CD 8+) comprises 8 to 10 amino acids of the p21 ras proto-oncogene protein including position comprise position 12 and/or 13, or position 61, of the p21 RAS proto-oncogene protein and have an amino acid substitution in position 12, 13 or 61. This document also discloses that the peptide may be used as a cancer vaccine and in compositions for anti-cancer treatment. However, no specific peptide mixtures are disclosed as being particularly useful.
Furthermore, neither of these documents discusses how particular peptides are associated with particular types of cancer, and do not address the redundancy of peptides in mixtures comprising a number of peptides.
Gjertsen et al. (Int, J. Cancer 2001, 92, p. 441-450) discloses a phase I/II trial involving patients with adenocarcinoma of the pancreas vaccinated with synthetic mutant RAS peptides in combination with granulocyte-macrophage colony-stimulating factor. This trial used single peptide vaccines or a mixture of four mutant peptides. The combination vaccine consisted of the four most common K-RAS mutations found in pancreatic adenocarcinoma, namely peptides having a G12V, a G12D, a G12C or a G12R mutation. However, this document does not disclose any other combinations of peptides that may be useful, does not disclose any other mutations of the RAS protein that are associated with cancer, and does not discuss how particular peptides are associated with particular types of cancer.
Wedén et al. (Int. J. Cancer 2010, 128(5), p. 1120-1128) reports the long-term follow-up of patients with pancreatic adenocarcinoma vaccinated with synthetic mutant RAS peptides. The vaccine consisted of either a single RAS peptide or a cocktail of seven RAS peptides. In particular, the seven RAS peptides used in this trial had a G12A, a G12C, a G12D, a G12R, a G12S, a G12V or a G13D mutation. However, this document does not discuss how particular peptides are associated with particular types of cancer, and does not disclose any other combinations of peptides which may be useful.
Hunger et al. (Exp. Dermatol. 2001, 10: 161-167) reports a clinical pilot study of the in vivo immunogenicity of RAS peptides with safety as the primary end point and immunogenicity of RAS peptides as a secondary end point. Melanoma patients were immunised intradermally with N-ras peptides 9 residue 49-73) with four codon 61 mutations. Eight of the patients showed positive responses. However, this document does not discuss how particular peptides are associated with particular types of cancer, and does not disclose any other combinations of peptides which may be useful.
Prior et al. (Cancer Res. 2012, 72(10), p. 2457-2467) discloses that different types of cancer are coupled to mutation of a particular RAS isoform and that each isoform has a distinctive codon mutation signature. In addition, Prior et al. discloses that a total of 18 mutations occur in positions 12, 13 and 61 of the RAS protein, with six mutations occurring in each position. This review also discusses the effects of these mutations on RAS function and the potential mechanisms leading to differential patterns of RAS isoform mutations. However, this document does not address the treatment or prophylaxis of cancer, or the issue of immunodominance and redundancy within a vaccine. In addition, there is no disclosure of a vaccine or treatment against cancer, and this document does not disclose any combinations of peptides which may be useful.
Thus, there is a need to provide further and more effective cancer vaccines and/or treatments. In particular there is a need to provide vaccines and/or treatments which are targeted to particular cancers, which overcome issues of immunodominance and redundancy, and which are cost-effective.